Catheter or electrophysiology ablation is an invasive cardiac procedure that uses radio-frequency (RF) energy or cyroablation to remove faulty electrical pathways from the heart of a person that is prone to developing cardiac arrhythmias such as atrial fibrillation. The procedure involves advancing several flexible catheters through the patient's blood vessels, usually via the femoral vein, internal jugular vein, or subclavian vein. The catheters are advanced into the heart and radio-frequency electrical impulses (or other ablation technique) are used to induce and/or study various arrhythmias, and ablate the abnormal tissue that is causing the arrhythmia, if deemed necessary.
Certain ablation procedures include extensive radiofrequency ablation of the left atrial posterior wall of the heart. Extensive radiofrequency ablation in this location carries the potential risk of collateral damage to structures adjacent to the left atrial posterior wall, including the esophagus. The most worrisome collateral damage is an atrial esophageal fistula, estimated to occur at a rate of approximately 0.5%; however, underreporting is likely, and the true incidence is unknown and could likely be higher. An atrial esophageal fistula is a rare, but almost always a lethal complication.
It is known to insert an esophageal probe into the esophagus of patient undergoing such an ablation procedure. The probe may include one sensor to measure the temperature inside the esophagus. A problem with such known procedures is that there is presently a high rate of esophageal injuries. The ongoing high rate of esophageal thermal injury, despite luminal esophageal temperature (LET) monitoring, is specifically related to the limitations of current techniques and medical devices used for LET monitoring. For example, there is often suboptimal orientation and positioning of the LET probe in relationship to the site of radiofrequency application in the heart, which results in an underestimation of the true LET and leads to esophageal injury due to unseen temperature rises. Current modalities reduce but do not eliminate left atrial-esophageal fistulas.
Esophageal injury is associated with a high mortality rate in addition to numerous co-morbidities. Studies have shown esophageal injury with mucosal changes consistent with thermal injury occurring at a rate as high as 50% after catheter ablation and up to 26% with necrotic and ulcer-like changes. Fistula formation is thought to occur due to conductive heat transfer to the esophagus that causes trans-mural tissue injury leading to a fistulous connection between the esophageal lumen and the left atrium, leading to sepsis, stroke and eventual death. From several studies, the point of biggest vulnerability for the esophagus to thermal injury from cardiac procedures is during ablation of the posterior left heart chambers, including the left atrium. This is due to its close anatomic position of the esophagus. Unfortunately, there is no clear method to accurately define the precise location of the esophagus. This is compounded by the fact that it is known from cadaveric and imaging studies that the anatomic relationship between the esophagus and left atrium (contact area) varies significantly between individuals and even within the same individual during the course of one procedure, as peristalsis and deglutition promotes esophageal movement.
Knowing that the esophagus is not a static organ and certainly not during a prolonged electrophysiological or surgical procedure there is a need for a medical device to overcome these problems. In addition, the esophagus is often compressed between the left atrium and surrounding structures, causing the esophagus to take a flattened and ovoid shape with a broad contact area to the posterior left atrial wall. Some studies have shown an expected broad contact area that spans the majority of the posterior left atrial wall. Therefore, the esophagus is essentially vulnerable to thermal injury during RF ablation from any location along the posterior left atrial endocardium.
Electroanatomic mapping systems, such as Carto by Biosense Webster and EnSite system by St. Jude Medical, allow a physician to non-fluoroscopically visualize catheters within a three dimensional reconstructed electroanatomic map of the heart that was created by means of intracardiac catheters. These systems are used to accurately visualize intra-cardiac catheters and manipulate them non-fluoroscopically, thereby decreasing radiation exposure to both the operator, patient, and bystander staff. These systems also display activation timing and voltage data to identify arrhythmias. For example, the EnSite system can incorporate and use any standard diagnostic catheter containing an electrode to create an electroanatomic map. The system localizes intra-cardiac catheters and builds a three dimensional map by collecting the electrical points from electrodes on a standard electrophysiology catheter measured within an impedance field created by patches placed on a patient. The EnSite technology is an open platform that is compatible with catheters from most manufacturers and can simultaneously display up to 12 catheters and 64 electrodes.
A three dimensional electro-anatomic shell is created when the intra-cardiac catheter collects various points while in contact with the cardiac endocardium as the physician manipulates the catheter. These points are electrical signals sensed by the electrodes on the catheter. The shell can then be continuously modified throughout the procedure by collecting additional points to decrease the amount of extrapolation and increase accuracy. Methods for creating the above mentioned three dimensional map of the heart are described in U.S. Pat. Nos. 6,226,542, 5,738,096, 5,546,951, 6,368,285, and 6,650,927.
Different strategies have been employed to reduce esophageal thermal injury with various means of monitoring the luminal esophageal temperature or esophageal anatomic location in relation to an intra-cardiac catheter. A disadvantage of these known systems and methods is that they do not provide live visualization of the probe itself within the anatomic shell of the esophagus.
Another disadvantage of known systems and methods is that it has not been possible to non-fluoroscopically visualize the location of a temperature sensor within the esophagus relative to the distal end of an intra-cardiac ablation catheter prior to each ablation, limiting the accuracy of the temperature readings. This problem is compounded because of variability in left atrial and esophageal anatomy, including the esophageal wall thickness.
A temperature sensor for insertion into the esophagus is known from U.S. Pat. No. 7,819,817. A disadvantage of this device is that it does not enable the creation of a live, continuously updating electroanatomic or thermal shell of the esophagus. Another disadvantage of the device disclosed in U.S. Pat. No. 7,819,817 is that it requires a permanent balloon for positioning the probe. The balloon serves to anchor the esophagus in one location and limits natural esophageal mobility; thus, increasing the potential for esophageal injury to that anchored location. A further complication from a balloon includes an increased risk for aspiration by obstructing the natural peristalsis of esophageal and pharyngeal secretions, increasing the risk for a severe pneumonia and respiratory failure. In addition, the balloon can cause great discomfort to the patient both on swallowing and with prolonged inflation during the procedure. The permanent cable and balloon add increased size and stiffness and increases the risk for trauma to the esophageal lumen.
Attempts at localizing the esophagus prior to the catheter ablation procedure have been employed with Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans. Unfortunately, studies have shown that despite these imaging modalities being performed within 24 hours of the procedure, there was still significant migration of the esophagus up to 15 mm in less than 24 hours. Thus, imaging the esophagus prior to the procedure is inadequate to locate the true and precise anatomic location of the esophagus.
An esophageal recording/pacing catheter for noninvasively pacing/recording the heart while affixed to an esophageal echocardiography probe is disclosed in U.S. Pat. No. 5,343,860. This device is a planar sheet that was designed solely to be affixed to an esophageal echocardiography probe. Clinical studies have shown that leaving an esophageal echocardiography probe in the esophagus throughout the procedure leads to a higher risk of esophageal-atrial fistulas. It is known that larger probes alter current density from the radiofrequency application in the left atrium and facilitate heating of the esophagus. Thus, it is not recommended to leave a transesophageal probe in the esophagus throughout an atrial fibrillation procedure in its entirety, precluding live and continuous esophageal temperature feedback and live visualization of the probe within the esophagus throughout the procedure.
A large surface area temperature sensing device has been proposed in US Patent Application No. 2010/0030098A1. A disadvantage of this device is that it is solely a temperature-sensing device and does not include any electrodes. In addition, the operator can not visualize this device within the esophagus in real time during the procedure due to the lack of electrodes; thus, precluding live feedback to the operator in regards to the relative distance between the esophageal device and the cardiac ablation catheter.
Attempts at cooling the esophagus have also been proposed, for example in US Patent Application No. 2007/0179537. However, clinical studies have shown that cooling systems are not effective in cooling the deep muscular layers of the esophagus, which are the initial sites of thermal injury in contact with the left atrium and serve as the origin for fistula formation. Thus, the catheter simply cools the exposed surface area of the esophagus, which is not only ineffective in protecting the esophagus but also causes great discomfort to the patient.
Proximity detection systems have been proposed through US Patent Application No. 2007/0106287. This system allows an esophageal catheter to communicate with a cardiac catheter and measure a proximity signal between the two catheters. A disadvantage of the type of system is that there is no direct visualization of the esophagus or atrium via an anatomic or thermal map. Furthermore, proximity is indicated by measured proximity signals, which can be inaccurate secondary to the anatomic variability between the two catheters. In addition, there can be persistent and latent heating up to sixty seconds after termination of ablation. In addition, studies have shown that heating of the esophagus can occur at a distance from an esophageal temperature sensor, as there is great diversity in individual esophageal anatomy. Though two catheters may be far in distance as judged by “proximity signals” there may be significant esophageal anatomy between the two catheters that will conduct the heat from the ablation catheter and promote esophageal injury through conductive heating.
U.S. Patent Application No 2006/0106375 discloses an esophageal catheter that is commercially available today as the EsoPhaStar. A disadvantage of this catheter is that it only provides a static esophageal map. It does not provide live and continuous temperature readings, nor does it allow for concomitant cardiac pacing or sensing or have the capability to create a live three dimensional and continuously updating esophageal thermal map.